1. Field of the Invention
The present invention relates, generally, to injection molding systems. More particularly, the invention relates to sequential multi-material Injection molding where the product produced has a portion made of one material and another portion made of a different material.
2. Background Information
The injection molding process and equipment are well known. Molten material is injected into a space formed between a mold cavity and a core that together form a mold. A plurality of mold cavities are mounted on a cavity plate and a corresponding plurality of cores are mounted on a core plate so they align with the cavities. The distance between the centerlines of any two adjacent mold cavities is known as the “mold pitch”. The injection molding machine typically moves the core plate relative to the cavity plate to open and close the mold between each “shot” of material into the mold to eject the molded parts. The parts typically remain on the core when the mold is opened and the parts are then ejected from the core.
Parts can be molded with different materials used for different portions of the part. The different materials may be, for example, different resins, or different colors of the same resin. To mold such parts, typically one portion is molded first, then that molded portion is transferred to a second cavity where the second portion is molded against the previously formed first portion. Such a processes described in U.S. Pat. No. 3,914,081 in which the cores are rotated between two molds, and U.S. Pat. No. 5,007,822 in which the cores are moved laterally between a first set of mold cavities and the second set of mold cavities. For molds having a large number of cavities, shuttling the cores laterally from one group of cavities to another group requires the set of cores to move a great distance along the mold. Such large movement takes time and thereby increases the molding cycle time, especially for large pitch molds or molds with a large number of cavities. Since such molds are fairly massive, their inertia influences the speed with which they can be safely moved in a molding machine.
Generally, it is desirable to reduce the molding cycle time as much as possible to maximize productivity. For multi-material molding, it is, therefore, desirable to minimize the time needed to shuttle cores from one set of molds to another. There is a need for a mold core shuttling system that can move from one set of cavities to another in a shorter time.